Analysing GORK clustering for enhanced stomatal control

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Stomata are pores that provide for gaseous exchange across the impermeable cuticle of plant leaves. They open and close to balance the requirement for CO2 entry for photosynthesis against the need to reduce the transpiration of water vapour and prevent leaf drying. Stomatal transpiration is at the centre of a crisis in water availability and crop production that is expected to unfold over the next 20-30 years: globally, agricultural water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is projected to double again before 2030. The bulk of water used in agriculture passes through the stomatal pore. Thus stomata represent an important target for manipulating crop performance. Significantly, stomatal responses are often delayed in the face of environmental fluctuations, especially of light. Improving water use efficiency (=amount of carbon fixed in photosynthesis/amount of water transpired) should be possible, without a cost to carbon assimilated in photosynthesis, if the speed of stomatal response can be enhanced.Stomatal movements are driven by solute transport - and consequent uptake/loss of water - across the cell membrane of the guard cells which surround the stomatal pore. Guard cells harbour ion channel proteins to facilitate cation flux for stomatal movement. Uniquely, the opening (or gating) of one class of plant ion channels is also sensitive to external K+ concentration. These channels are found in guard cells of tobacco, Vicia and Arabidopsis, in the latter encoded solely by the GORK gene. Increasing K+ outside moderates channel opening in parallel with the equilibrium voltage for K+ and affects whole-cell conductance. These channels are the main pathway for K+ efflux during stomatal closure, but their K+-sensitivity constrains K+ flux capacity, notably at higher external K+. Estimates based on recent modelling suggests that stomatal closure could be accelerated 3-fold with only a moderate increase in the flux capacity of these channels.The K+-sensitivity of the GORK channel is a property of the channel protein itself, which should facilitate manipulating K+ efflux capacity to accelerate stomatal closure. My laboratory has uncovered evidence that the K+-dependence of GORK gating is associated with its assembly in clusters. These assemblies require the the so-called 'voltage-sensor domains' (VSDs) of GORK to interact with one another. Movement of the VSDs is known to couple voltage to channel gating, so it is likely that interaction between VSDs provides a mechanism for cooperative self-regulation. I propose now to complete the analysis of GORK VSD interaction and the consequences for channel control and for stomatal movements. Regardless of the mechanism, it is clear that these discoveries offer the means to explore a unique and fundamental property of this class of K+ channels in plants and to manipulate channel activity, potentially enhancing the kinetics of stomatal closure and water use by the plant.